Drive mechanism for the intermittent movement in a television motion-picture projector



Aug. 24, 1948. F. J. BINGLEY 2,447,339

DRIVE MECHANISM FOR THE INTEHMITTENT MOVEMENT IN A TELEVISION MOTIONPICTURE PROJECTOR Filed Sept. l1, 1945 Patented Aug. 24, 1 948 DRIVEMECHANISM FOR THE INTEBMIT- TENT MOVEMENT IN A TELEVISION MO-TION-PICTURE PROJECTOR Frank J. Bingley, Philadelphia, Pa., assignor, bymesne assignments, to Philco Corporation, Philadelphia, Pa., acorporation of Pennsyl- Vania Application September 11, 1945, Serial No.615,671

5 Claims. 1

This invention has to do with television and particularly with motionpicture projectors adapted for use in'television broadcasting systems.

For various reasons known to those skilled in the art, televisioncameras are designed to generate television signals at the rate of 60fields per second, interlaced, or, in other words, 30 complete framesper second. On the other hand standard motion picture projectors aredesigned to expose 24 frames per second. Therefore, when transmittingstandard motion picture nlm by television, it is necessary to do so bysome method rwhereby the scanning rate of the television system is-correlated with the normal exposure rate of the film so that adesirable reproduction will appear at the television receiver.

There are several methods by which this may be accomplished, only one ofwhich, however, so far as applicant is aware, makes use of intermittentlm motion for advancing successive frames into position to be projectedupon the screen of the cathode ray tube. Such intermittent motion framefor each complete revolution thereof and, as stated above, at the rateof 24 frames per second, when employed in motion picture practice.

To correlate the different rates of scanning and projection, as betweenthe television camera andthe motion picture projector, respectively,Bedford makes use of a varying rate of exposure for successive lmframes. To accommodate the 60 fields per second scanning rate of thetelevision projector to the 24 exposures per second of the motionpicture projectors, he projects (at the rate of one projection for eachone-sixtieth of a is employed in interlaced systems of scanning. and

it is with this type of apparatus that the present invention isprimarily concerned.

Such a. system is the subject of Patent No. 2,082,093, issued June 1,1937, to A. V. Bedford, and also of an article entitled Application ofmotion-picture film to television, by E. W. Engstrom etal., andappearing, beginning with page 48, in the RCA Review, volume 4, 1939-40.The system disclosed in these publications has been adopted in the artas being the best previously known method for broadcasting standardmotion picture nlm by television. Its operation, however,

' depends upon a modification of the well known Powers intermittentmovement. This movement has proved disadvantageous because of itsunreliable operation and high manufacturing cost.

When used in standard motion picture projection machines the Powers camhas only one lobe for turning the nlm sprocket, which is movedone-quarter of a revolution for each complete revolution of the cam.This quarter of a revolution is accomplished at high speed and moves thenext frame into position to be projected upon the screen at the time thesolid portion of the shutter is passing through the light beam of theprojector. Ihe high speed is necessary to permit each frame to remain atrest in projection position for as long a period oftime as possible.Thus we see that an unmodied Powers intermittent movement normallyexposes one picture second) an image of each odd motion picture frametwice in succession upon the mosaic screen of the cathode-ray, or cameratube, and an image of each even frame three times upon the screen, allduring stationary periods of the film.A

Correct timing of these projections upon the screen, as taught in theBedford system, is accomplis'hed by modifying the Powers intermittentmovement to include on the cam two lobes spaced 144 degrees apart. Thusfor each Ysingle revolution of the cam, two frames will have' moved intoposition for projection necessitating a lreduction in the R. P. S. ofthe intermittent movement to twelve instead of the normal twen--ty-four. For each revolution of the intermittent movement two framesare exposed or projected for scanning, one of which is scanned twice(consuming two-sixteths of a second) during the time the follower ispassing through the 144 angle between the lobes, and the other isscanned three times (consuming three-sixtieths of a second) during thetime the follower is passing through the remaining angle of 216.Therefore, at the end of each twelve revolutions of the cam, and at theend of each second, a total of sixty fields have been scanned for eachtwenty-four frames of motion pictures exposed.

One of the chief faults found in this system is the necessary reductionby one-half in the number of revolutions per second, which increasestwo-fold the pull-down time for moving each successive frame intoposition for projection and decreases to an undesirable degree, theworking tolerances, i. e., the time between pull-down and exposure.

The Powers intermittent movement is no longer widely used in motionpicture projectors. Its use in television has been tolerated,heretofore, only for want of `a better system in which the moredesirable intermittent movements may be incorporated, and hence, withthe foregoing in mind, it is an important object of the presentinvention to provide an improved motion picture 3 projector for use intelevision broadcasting systems.

Another important object of the invention is the provision of such aprojector in which standard, unmodified, intermittent movements may beemployed.

A further object of the invention is to provide such a projector whichis characterized by its simplicity and its efficient mode of operation.

To the foregoing general ends the present invention proposes to use anunmodified intermittent movement, but to modulate the velocity of itsdriving shaft so that, while its average rotation is the normal 1440 R.P. M., or 24 R. P. S., successive revolutions are faster and slower,respectively, with the result that pull-downs will occur at appropriateintervals, permitting two projections of the odd'frames upon the mosaicscreen of the camera tube during the fast revolutions, and threeprojections of the even frames upon the screen during the slowrevolutions, at the rate of sixty projections per second of twenty-fourpicture frames.

It will now be well understood that, prior to this invention, televisiontransmission of standard motion picture lm, as far as the intermittentfilmmotion types are concerned, has been completely dependent upon theaforesaid modied Powers intermittent movement, but that with theintroduction of the present invention the necessity for using thismodified intermittent movementv is eliminated, and the use of the moredesirable intermittent movements, such as, for example, the well knownand superior Geneva" movement, is made possible. It should be furtherunderstood however, that, as a result of the present invention, any ofthe well known intermittent movements, including the unmodied Powers,may conveniently be used in the projector of the instant invention. Whenthe "Powers movement is employed, in conjunction with the apparatus ofthe present invention, the necessity of reducing the normal R. P. S. byhalf, is obi/lated.

In the drawings:

Figure 1 illustrates diagrammatically the preferred embodiment of theinvention;

Figure 2 is a sectional view on an enlarged scale, taken substantiallyas indicated bythe line 2-2 in Figure 1;

Figure 3 is a fragmentary view on an enlarged scale, and partially insection, illustrating the preferred Geneva type of intermittentmovement; and,

' Figure 4 is a sectional view taken substantially as indicated by theline 4--4 in Figure 3.

More specifically, and with particular reference to the details inFigure 1 of the drawings, the numeral IIJ designates a motion-pictureprojector adapted to project successive picture images intermittentlyupon a photo-sensitive screen II of a cathode ray, or camera tube I2,positioned within a television camera I3. Each of these images isscanned in the usual well known manner by a moving beam of electrons,developed ,in the electron gun It .if tube I2, thus to generate thenecessary picture signals for broadcast by the transmitter (not shown).

As pointed out heretofore, when broadcasting standard motion picturefilm by television it is necessary to correlate the exposure speed of 24frames per second for normal motion picture projection with the scanningrate of 60 elds per second for television systems. In the presentinvention this correlation is accomplished in the novel mannerhereinafter described.

The motion picture film I5 is moved into projection position in the filmgate i511, intermittently, at the rate of twenty-four frames per secondby a. pull-down sprocket I6 which is operated by a standard intermittentdevice II. As illustrated, this device is of the highly desirable Genevatype, although it should again be clearly understood that any suitablestandard intermittent movement may be used, such as, for example, thestandard unmodified Powers type above referred to. These intermittentmovements are well known in both the motion picture and television artsand it is believed that a detailed description thereof is unnecessary toa complete understanding of the present invention. However, a briefdescription of the Geneva" type illustrated, will serve to point out itssalient features as related to the present invention.

With particular reference to Figures 3 and 4, which illustrate the typeof Geneva intermittent movement best serving the purposes of theinvention, the numeral I8 designates the housing therefor, while theintermittent movement itself consists of a Maltese cross I9, morecommonly referred to as the star, and a cam 20 upon which is mounted amaster pin 2|, adapted to drive the star. This cam is also provided witha at circular surface, or cam ring 22, by means of which the star, andtherefore the intermittent sprocket I6, both of which are mounted uponshaft 23, are locked in a fixed position while the star is not beingdriven by pin 2 I, that is, during the interval the frame is inalignment with the aperture in position to be projected upon the screenI'I.

The action of the movement is as follows:

The cam carrying the master pin is continuously rotated as long as theprojector is in motion, as will be more fully explained hereinafter.During the major portion of the operating time the star is maintainedmotionless, by virtue of contact between one of its four curved surfaces24, and the adjacent surface of the cam ring 22. Under this condition itis evident the star cannot be rotated. It must, in fact, remainperfectly still until the two surfaces are released. In this conditiontheA movement is said to be on the lock. Remembering that the camrotates continuously in the direction indicated by the arrow, it isevident that presently the' pin will engage one of the slots 25 in thestar and, at that instant, surface 24 will be out of contact with ring22 and free to rotate under the control of pin 2 I.

As the pin enters one of the star slots 24 it moves the star one-quarterof a revolution. The movement i-s very rapid but, nevertheless, movementof the star and the associated sprocket are initiated slowly, the speedgradually being increased to maximum. The star and sprocket then slow,gradually, to a full stop, whereupon surface 24 and ring 22 re-engage,locking the star. 'I'he picture is projected and the cycle of action isrepeated.

In particular accordance with the present invention, the intermittentmovement is driven at the rate of twenty-four revolutions per secondwith alternate, or odd revolutions, of shorter duration than the evenones. As stated heretofore, television cameras are designed to scansixty fields per second and, therefore, in my apparatus the fasterrevolutions are preferably of twosixtieths of a second duration, whilethe slower revolutions are of three-sixtieths of a second duration. Thusit is seen that of the twentyfour frames scanned by the camera, twelveare scanned twiceror ,for two-sixtieths of a second each, which equalstwenty-four-sixtieths of a second, while the remaining twelve are eachscanned three times, or for three-sixtieths of a second each, whichequals thirty-six-sixtieths of a second. From these ngures it is obviousthat for each second of time twenty-four motion picture frames, which is'the standard practice in motion picture art, are scanned sixty times,which is in accordance with television practice.

It is now evident that the different operating speeds normal to each ofthese arts may be thus correlated, by properly modulating the velocityof the shafting which drives the intermittent movement. j

Means for driving the intermittent movement in the desired manner isprovided by the associated mechanism illustrated in the drawing and nowto be described.

With reference to Figures l and 2, a motor 30 is provided for driving ashaft 3l which extends through a gear box 32 and has attached to itsfree end the usual shutter 33 provided with a pair oi' opposed apertures34 and 35. Also attached to the shaft 3l, on the portion within the gearbox, is a worm 35 adapted to rotate an associated pinion gear 31 mountedon a shaft 38. Shaft 3l extends transversely through a bearing block 38and has a disk 40 attached to its other end.

Disk 40 is provided with atransverse slot 4i into which one end of a pin42 (which is secured to the side wall of a gear 43) is adapted to nt fortransverse kslidable movement therein. Gear 43 is journalled in anotherbearing block 44 at a point onset from axial alignment with shaft 33, asshown at 45 (Figure 2) by the extended parallel lines 43 and 4l passingthrough the centers of disk 40 and gear 43. By reason 'of this onset ofthe centers of rotation of disk 40 and gear 43, when the disk isrotating, the angular velocity of the gearis modulated as describedheretofore. In other words, for each revolution of disk 40, at a.constant speed, gear 43 will rotate through substantially one-halfrevolution at a speed greater than that of the following half.

Mounted adjacent one end of a shaft 50, and intermeshed with gear 43, isa gear 5l having a diameter equal to one-half the diameter of gear 43and providing a resultant two-to-one ratio between the driving anddriven shafts. For each complete revolution of gear 43, gear 5| willrevolve twice and, as the speed of rotation of gear 43 has beenvelocity-modulated as described, gear 5l will move through one of itstwo revolutions at a greater velocity than will obtain during thesucceeding revolution.

Shaft 50 passes through a bearing 52 on housing Il and into the interiorof the intermittent movement I1. A gear 53 is attached to the end o! theshaft and is intermeshed with a similar gear 54 to which is secured theintermittent cam 25. A shaft 55, upon which gear 54 and cam 20 aremounted for rotational movements, is also joui-nailed in bearing 52.

It will now be clearly understood that shaft 50, and consequently gear53 attached thereto, are being driven with modulated velocity, theduration of successive revolutions alternating between two-sixtieths andthree-sixtieths of a second. The intermittent movement is, of course,driven correspondingly, through gear 54 to which the cam 20 is attached.Thus the desired variation in interval between successive pull-downactua- A anmactions is achieved in a novel and advantageousv the presentinvention provides a simplified, efii-` cient and improved motionpicture projector in which standard intermittent movements may beadvantageously employed.

As employed herein, the words standard intermittent movement areintended to denote A those types commonly employed in motion pictureprojectors and normally constructed and arranged to effect nlm pull-downat equal time intervals. Both the Geneva movement and the so-calledunmodined Powers movement, I

referred to hereinabove, are exemplary of the class of devices coveredby the term. I

It should be borne in mind that while the velocity variation, ormodulation, of the present invention enables the use of standardunmodiiied intermittent movements, and is therefore advantageous; in abroader aspectthe modulation l taught is not limited in applicability touse with such movements only. However, it will be understood that suchapplications of the invention and modifications therein arecontemplated, as may come within the termsl of the appended claims.

I claim: j

1. In a motion picture projector, film advancing means, and actuatingmeans for operating said nlm advancing meansso as intermittently to movesuccessive nlm frames into position for projection, said actuating meansincluding: a continuously rotating member, an element discontinuouslyrotated thereby, velocity modulating means for causing successivecomplete revolutions of said continuously rotating member to occur atfaster and slower rates, alternately, whereby correspondingly to varythe time interval between successive discontinuous rotations of saidelement, and means drivingly interconnecting said discontinuouslyrotated element and said nlm advancing means to effect movement ofsuccessive frames into position for projection after intervals ofgreater and less duration.

2. In a motion picture projector, film advancing means, and actuatingmeans for operating said nlm advancing means so as intermittently tomove successive nlm frames into position for projection, said actuatingmeans including: a continuously rotating member. an elementdiscontinuously actuated thereby once for each revolution of saidcontinuously rotating member, velocity modulating means for causingsuccessive complete revolutions of said continuously rotating member tooccur at faster and slower rates, alternately, whereby correspondinglyto vary the time interval between successive discontinuous actuations ofsaid element, and means drivingly interconnecting said discontinuouslyactuated element and said nlm advancing means to effect movement ofsuccessive frames into position for projection after intervals ofgreater and lesser duration.

3. A construction in accordance with claim 1 and further characterizedin that the successive complete revolutions of said continuouslyrotating member are completed in time increments alternating betweentwo-sixtieths and threesixtieths of a second.

ananas 4. In 'a motion picture projector for use in television broadcastsystems, 111m pull-down means, an intermittent movement coupled to saidfllm pull-down means and eective to operate said means so as to movesuccessive 111m frames intermittently into position to be projected forscanning, said movement including a continuously rotating element and anim-actuating member discontinuously operated thereby upon completion ofveach revolution oi said con tinuously rotating element, a substantiallyconstant speed prime mover, and variable speed apparatus coupling saidprime mover to said continuously rotating element and so driving saidelement that successive complete revolutions thereof occur atalternately greater and lesser velocities.

5. In a motion picture projector for use in television broadcastsystems, film pull-down means, a Genevatype intermittent movementcoupled to said lm pull-down means and effective to operate said meansso as to move successive film frames intermittently into position to beprojected for scanning, said movement in cluding a continuously rotatingcam and aillmactuating star wheel discontinuously operated by `said camupon completion of each revolution thereof, a substantially constantspeed prime mover, and variable speed apparatus mechanically couplingsald prime mover to said cam and effective to drive said cam so thatsuccessive complete revolutions thereof occur at alternately greater andlesser velocities.

J. BINGIEY.

nEFanaNoEs CITED The following references are of record in the ille ofthis patent:

UNITED STATESv PATENTS

